Timepiece movements that match the above definition are already known. CH Patent No. 7965, in particular, discloses a movement of this type with reference to drawings, one of which is reproduced in FIG. 1 annexed to this document. The movement disclosed includes a going train of which only the last two wheel sets are shown. There is a wheel set formed by the third pinion and the third wheel (respectively referenced G and H), and the wheel set formed by the fourth pinion and wheel (respectively referenced A and C). The document specifies that the fourth wheel (or intermediary wheel) C drives the escape (not shown) in a known manner. Moreover, the escape and the balance E are mounted on a platform F. The bottom surface of platform F has a thick cylindrical pivot B which is inserted to rotate in an aperture of a plate P. Cylindrical pivot B is hollow and shaped to let the arbour of the fourth wheel set pass through it, so that platform F and the fourth wheel rotate about the same axis. Finally the third pinion G is for driving platform F in rotation, via a wheel D, which is pierced in the middle and screwed to the platform, concentrically to the axis of rotation of said platform.
In the example disclosed by this prior art document, third wheel H is driven in quite a conventional manner at a speed of one revolution per 7½ minutes. Third pinion G has seven times fewer teeth than wheel D with which it meshes, and platform F therefore competes one revolution every 52½ minutes. Moreover, fourth pinion A has 7½ times fewer teeth than third wheel H. Fourth pinion A thus conventionally completes exactly one revolution per minute. Since the rotational speed of fourth wheel C is determined by the escapement, which itself rotates, with platform F, in the same direction as fourth wheel C, the frequency of balance E has to be decreased by approximately 2% to take account of the speed of platform F.
Those skilled in the art will have recognised a karussel in the above description. Upon reading this description, it is clear that the karussel mechanism is completely different from a tourbillon mechanism. Indeed, as in an ordinary watch, with a karussel, the energy from the barrel is transmitted to the escape wheel via the fourth wheel. The movement drives the platform via an additional gear, and if this gear is uncoupled, the watch can continue to function while the platform is no longer rotating.
According to the work entitled, “La montre: principes et méthodes de fabrication” (pages 298-9), the karussel compensates for poising defects in the balance just as well as the tourbillon. Moreover, it is easier to make and produce in large quantities. However, for watch specialists and collectors the tourbillon is more attractive to look at. It is therefore an object of the present invention to provide a timepiece movement fitted with a karussel that has the same aesthetic qualities as a tourbillon. The invention achieves this object by providing a timepiece movement in accordance with the following disclosure.